Methylene chloride stabilized with tetrahydrofuran

ABSTRACT

Tetrahydrofuran and optionally propylene oxide in admixture with methylene chloride have been found to prevent degradation of methylene chloride in the presence of metals, metal halides, combinations thereof, and aromatic compounds, which react with methylene chloride in the presence of said metals, metal halides and combinations thereof. Reactions of aliphatic organic compounds with said metals, metal halides and combinations thereof to form products which result in deterioration of methylene chloride are also inhibited. A method for vapor degreasing metals by using the stabilized methylene chloride is described.

Beckers 1 Jan. 14, 1975 METl-IYLENE CHLORIDE STABILIZED WITH TETRAHYDROFURAN [75] Inventor: Norman L. Beckers, Chardon, Ohio [73] Assignee: Diamond Shamrock Corporation,

Cleveland, Ohio 221 Filed: Feb. 23, 1973 21 Appl. No.: 335,365

[52] U.S. Cl. 260/6525 A, 252/171, 252/407, 134/31, 134/40 [51] Int. Cl. C07c 17/40, C07c 17/42 [58] Field of Search 260/6525 R; 252/170, 171

[56] References Cited UNITED STATES PATENTS 2,998,461 8/1961 Campbell 260/6525 R 3,070,634 12/1962 Hardies et a1 260/6525 R 3,285,857 11/1966 Rathbone et al 260/6525 R Y 3,326,988 6/1967 Stack 260/6525 R 3,326,989 6/1967 Cormany et al. 260/6525 R 3,423,476 1/1969 Patron 260/6525 R 3,670,036 6/1972 Vivian 260/6525 R Primary Examiner-Howard T. Mars Attorney, Agent, or Firm-William A. Skinner [57] ABSTRACT Tetrahydrofuran and optionally propylene oxide in admixture with methylene chloride have been found to prevent degradation of methylene chloride in the presence of metals, metal halides, combinations thereof, and aromatic compounds, which react with methylene chloride in the presence of said metals, metal halides and combinations thereof. Reactions of aliphatic organic compounds with said metals, metal halides and combinations thereof to form products which result in deterioration of methylene chloride are also inhibited. A method for vapor degreasing metals by using the stabilized methylene chloride is described.

2 Claims, No Drawings METHYLENE CHLORIDE STABILIZED WITH TETRAHYDROFURAN BACKGROUND OF THE INVENTION Methylene chloride is a highly versatile and useful solvent for various industrial applications at both normal and elevated temperatures. A particularly important industrial use is the vapor degreasing of metals. Methylene chloride is known to be more stable than other chlorinated hydrocarbons solvents such as perchloroethylene, trichloroethylene and methyl chloroform when the solvents are used in unstabilized condition. For example, methylene chloride is more resistant to oxidation, hydrolysis and pyrolysis than other chlorinated solvents and does not substantially react with aluminum in the aluminum scratch test commonly used to indicate unstabilized or methyl chloroform. In addition, methylene chloride may be used to greater advantage in vapor degreasing of metals than other known degreasing solvents since it may be used effectively at lower temperatures due to its lower boiling point and excellent stability. Methylene chloride is particularly desirable for such degreasing operations since it is substantially resistant to photochemical activity and therefore does not contribute to air pollution by smog formation. However, methylene chloride when used in various metal cleaning functions, including vapor degreasing, suffers the disadvantage of being reactive with aromatic compounds in the presence of metals, metal halides and combinations thereof, including aluminum, zinc and iron, halides thereof, and combinations of said metals and halides which react with the methylene chloride to produce hydrochloric acid and objectionable high boiling tarry substances which render the methylene chloride unsuitable for further use. The entire reaction of methylene chloride in the presence of aromatic compounds is not completely understood but is believed to be a condensation reaction catalyzed by metal, metal halides or combinations thereof. Thus, the aromatic compound reaction with methylene chloride is believed to be catalyzed or initiated and catalyzed by the presence of metals such as aluminum, zinc, iron and the like, halides of said metals and combinations of said metals and halides. Such reactions are thought to be of the nature of a Friedel- Craft type reaction. Methylene chloride also disadvantageously suffers degradation by reaction of aliphatic organic compounds such as trans-dichloroethylene, l,l,l-trichloroethane and carbon tetrachloride with said metals, metal halides and combinations thereof. The reaction products are colored tar-like masses which render the methylene chloride unsuitable for use as a solvent, particularly in vapor degreasing of metals. Aromatic and aliphatic organic compounds of this nature and metals such as aluminum, iron and zinc, their halides and combinations are generally introduced into the methylene chloride from various cutting oils and lubricants used in metal fabricating operations which are carried over into the methylene chloride solvent during vapor degreasing or other cleaning of the fabri cated metal parts. Solvent manufacturing, handling and storage equipment is another source for introduction of such impurities. To prevent degradation and other types of deterioration such as oxidation, hydrolysis and pyrolysis which may occur in some instances, it has been the practice to incorporate minor quantities of various organic compounds into methylene chloride,

which compounds act as stabilizers to substantially prevent such degradation. It is desirable to provide methylene chloride stabilized to effectively prevent degradation in various applications, and the demand still exists for a low cost stabilized methylene chloride composition that can be easily prepared and which provides optimum stabilization under many different operating conditions.

SUMMARY OF THE INVENTION An object of this invention is to prevent deterioration or degradation of methylene chloride in association with metals, metal halides and combinations thereof including aluminum, iron and zinc, halides of said metals, combinations thereof, and an aromatic compound capable of reacting with methylene chloride in the presence of said metals, metal halides and combinations.

Another object of this invention is to prevent deterioration or degradation of methylene chloride in association with metals, metal halides and combinations thereof, including aluminum, iron and zinc, halides of said metals, combinations thereof and an aliphatic organic compound capable of reacting with these metals, metal halides and combinations thereof in the presence of methylene chloride.

A further object of this invention is to provide a stabilized methylene chloride composition in which the stabilizers are low in cost and capable of being incorporated with ease into the methylene chloride.

A still further object of this invention is to provide a process for the degreasing of metals by contacting the metals with methylene chloride stabilized to prevent degradation of the methylene chloride in the presence of metals, metal halides and combinations thereof, ineluding aluminum iron and zinc, halides of said metals, combinations thereof and aromatic compounds which react with the methylene chloride in the presence of said metals, metal halides and combinations.

Still another object of this invention is to provide a process for the degreasing of metals by contacting the metals with methylene chloride stabilized to prevent degradation of the methylene chloride in the presence of an aliphatic organic compound which reacts with metals including aluminum, iron, zinc and the like, halides of said metals and combinations of the individual metals and salts thereof.

These and additional objects of the present invention will become apparent to those skilled in the art from the description and claims which follow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The objects set forth above have been found to be attained by providing a composition consisting essentially of methylene chloride containing stabilizing amounts of from about 0.05 to about 2.0 percent by weight of the methylene chloride of tetrahydrofuran and optionally of propylene oxide.

The quantity of the stabilizing agents useful in the practice of this invention will vary depending upon the conditions of use, the identity and quantity of other sta bilizers incorporated into the methylene chloride and other practical operating considerations. Each stabilizing agent or compound may generally be used within the range of from about 0.05 to about 2.0 percent and preferably from about 0.10 to about 1.0 percent by weight of the methylene chloride. Although higher concentrations may be used, if desired, no additional benefit is obtained and the cost is unnecessarily increased. While the above composition containing stabilizing agents provides optimum prevention of degradation of the methylene chloride under a variety of operating conditions it is also possible to stabilize methylene chloride by deleting the propylene oxide depending on the stabilization required for the particular operating condition.

The stabilized composition may be used for the degreasing of metals by contacting the metals with the stabilized composition. It is also possible to use the stabilized methylene chloride composition for degreasing metals by deleting the propylene oxide. Thus, the process for vapor degreasing metals comprises contacting the metals to be degreased with the above described stabilized methylene chloride compositions wherein the methylene chloride contains either tetrahydrofuran only or an admixture of stabilizing amounts of tetrahydrofuran and propylene oxide.

In degreasing metals with the above described preferred stabilized methylene chloride in the presence of an aromatic compound which reacts with methylene chloride in the presence of metals, metal halides and combinations thereof including aluminum, iron, zinc, halides of said metals and combinations, there exists upon contact of the metal with the stabilized methylene chloride a composition comprising methylene chloride, a stabilizing amount of from about 0.05 to about 2.0 weight percent of the methylene chloride of tetrahydrofuran, optionally from 0.05 to about 2.0 percent by weight of propylene oxide, and an organic compound which reacts with methylene chloride in the presence of said metals, metal halides and combinations. The metals, metal halides and combinations may be present from any source such as chloride formed by drilling or other machining of aluminum or aluminum-containing materials with various working fluids such as cutting oils, lubricants and the like, or aluminum chloride may be present from the reaction of methylene chloride with aluminum. The reactive aromatic compounds include toluene, mesitylene, (trimethyl benzene), durene, (tetramethyl benzene), naphthalene, and the like. The reaction of methylene chloride in the presence of aliphatic organic compounds such as transdichloroethylene, carbon tetrachloride and 1,1 ,ltrichloroethane, metals, metal halides and combinations may also be inhibited by methylene chloride stabilized with the same amounts of tetrahydrofuran and optionally propylene oxide as above described.

In order that those skilled in the art may readily understand the present invention and certain specific embodiments by which it may be carried into effect the following illustrative examples are presented.

In Examples 1 and 2, respectively, of Table I, 15 ml of substantially water-free methylene chloride and 'methylene chloride stabilized with 2.8 percent wtqof tetrahydrofuran respectively, were placed in glass vials containing a 1 cm aluminum coupon one sixty-fourth inch thick. The vials were tightly capped and allowed to stand at ambientv conditions. After 16 hours no changes had taken place in the appearance of the solvent, the pH or the aluminum in each vial. Toluene in an amount of 5 percent by volume and about 0.04 grams of anhydrous aluminum chloride were then added to each via], the contents stirred, any changes in the appearance recorded, and the vials loosely capped and allowed to stand. After 4 hours and after 22 hours changes in the appearance of the aluminum coupons and the solvents, and relative pH values ofthe solvents, were recorded. The procedure of Examples I and 2 was followed in Examples 3 to 7 of Table I. In the latter Examples various compounds reported in the prior literature to be useful in stabilizing chlorinated solvents were evaluated for their ability to stabilize methylene chloride. In Examples 3 to 7 after the tightly capped vials had been standing for 16 hours no changes had occurred in the appearance of the solvent the pH or the aluminum coupons. The results ofthe tests of Examples 1 to 7 are set forth in Table I.

From Table I it will be readily observed that after 4 hours the methylene chloride without tetrahydrofuran had undergone a degradation reaction resulting in a dark orange coloration, evolvement of hydrogen chloride gas and complete loss of utility of the solvent. Examples 3 to 7 inclusive of Table I show that various compounds frequently used as solvent stabilizers are not as effective as tetrahydrofuran in inhibiting degra- TABLE I INHIBITION OF REACTION OF AROMATIC COMPOUNDS WITH METHYLENE CHLORIDE Upon Addition of 5% Vol. Toluene TABLE I -Continued INHIBITION OF REACTION OF AROMATIC COMPOUNDS WITH METHYLENE CHLORIDE Upon Addition of 5% Vol. Toluene Example Solvent and 0.04 grams After After No. System Aluminum Chloride 4 Hours 22 Hours 4 Methylene Solution Dark Purple Solution Black Chloride Colored Purple- Precipitate Containing black and Solution Aluminum Coupon Precipitate Yellow- Stabilized With Present Green 0.7 Wt. pH about 3.5 pH about Methyl Butynol 4.5 5 Methylene Light Lavender Solution pH about Chloride Precipitate Dark Gray 4.5 Containing And Precipi Aluminum Coupon tate Present Stabilized With pH about 3 28 Wt. l,l-Dimethoxyethane 6 Methylene Yellow Green Yellow White Chloride Precipitate Precipitate Precipitate Containing On Aluminum Solution Aluminum Coupon Coupon Yellow Stabilized With Solution pH about Wt.% Green-G ray 4.5 l,3Dioxolane pH about 3.5 7 Methylene Red Precipitate Orange Pink-Brown Chloride Precipitate Precipitate Containing On Aluminum Solution Aluminum Coupon Coupon Colorless Stabilized With Solution pH about 0.8 Wt. Colorless 4.5 1,4-Dioxane pH about 4.0

dation of methylene chloride by reaction of aromatic of the methylene chloride was added to the methylene compounds with methylene chloride in the presence of metals, metal salts and combinations thereof.

In Examples 8 to 13 of Table II, below, an aluminum reflux stability test was carried out by placing 100 ml of substantially water free methylene chloride in a flat bottom 300 ml boiling flask fitted with a condenser. One strip of aluminum about 1 /2 X 9 cm was inserted in the liquid in the flask and another about 1% X 6 cm was suspended in the condenser. During the extended period of reflux the solvent vapor surrounded, condensed, and dripped from the suspended strip onto the other partially immersed strip. The aluminum coupons were weighed initially. The methylene chloride was refluxed for a varying period of days. Various aliphatic organic compounds were individually added to the methylene chloride including vinylidene chloride, trans-dichloroethylene, chloroform and carbon tetrachloride, respectively. Combinations of all four compounds were also added to the methylene chloride in an amount of about 0.5 percent by volume. In Example 13 tetrahydrofuran in an amount of 0.5 percent by weight chloride containing the combination of the four aliphatic organic compounds. In all cases the pH and acid content, as HCl, were determined on the aqueous phase following extraction of the solvent with an equal volume of neutral distilled water and after the system was refluxed for varying time periods; also the aluminum coupons were cleaned, dried and weighed to determine the loss in weight, if any. In Examples 14 to 18 inclusive, 200 ml of methylene chloride were refluxed in a similar manner as in Examples 3 to 8 except no aluminum condenser coupon was used and the coupons in the flask were not weighed, with the exception that in Example 18 an aluminum coupon was inserted into the condenser for the last 3 days of reflux.

In examples 14 to 18 an amount of 5 percent by volume of a commercially available stabilized vapor dcgreasing grade of 1,1,l-trichloroethane was added to ml. of methylene chloride.

The results of the various tests are shown in Table II below.

TABLE 11 EFFECT OF ALIPHATIC ORGANIC COMPOUNDS ON ALUMI NUM REFLUX STABILITY TESTS OF METHYLENE CHLORIDE Example Volume Days Acid as Total mg Color of No Solvent System Additive Reflux pH ppgil Al loss Solvent H 8 Methylene 0.5% Vinylidene 23 7.0 0 0.2 Clear and Chloride Chloride (VDN) colorless 9 Methylene 0.5% Trans-dichloro 23 4.9 173 65.6 Yellow Chloride ethylene (T-DCE) l0 Methylene 0.5% Chloroform 23 7.0 0 0.3 Clear and Chloride colorless ll Methylene 0.5% Carbon Tetra- 6 5.1 46 53 Pink Chloride chloride l2 Methylene 0.5% VDN l3 4.8 U0 l2.l Purple- Chloride 0.5% T-DCE black 05% CHCl 0.5% CCl TABLE II Continued EFFECT OF ALIPHATIC ORGANIC COMPOUNDS ON ALUMI- NUM REFLUX STABILITY TESTS OF METHYLENE CHLORIDE Example Volume Days Acid as Total mg Color of No. Solvent System Additive Reflux pH ppn Al loss Solvent I3 Methylene 0.5% VDN 23 7.0 0 Clear and Chloride 0.5% T-DCE colorless Plus 0.5% 0.5% CHCl, by weight 05%CCl Tetrahydrofuran I4 Methylene 5% l,l,l-Tri- [/3 3 (HCl (Corro- Black sion) Chloride chloroethane Fumes) l5 Methylene 5% 1,l,l- 9 7.0 None (No Clear and Chloride Trichloroethane Corrosion) Colorless Plus 0.25% by weight Tetrahydrofuran (No l6 Methylene 5% l,l,l- 9 7.0 None Corrosion) Clear an Chloride plus Trichloroethane Colorless 0.25% by wt. Tetrahydrofuran and 0.25% by wt. Propylene Oxide (No Clear and 17 Same as Example 5% 1,1,1- 11 7.0 None Corrosion) Colorless 16 with addition Trichloroethane of about 0.04 g. anhydrous MCI and two additional days of reflux 18 Same as Example 5% 1,1,1- 14 5.0 (No Clear 17 with addition Trichloroethane Corrosion) and of about 0.04 g. yellow anhydrous FeCl;, and three additional days of reflux Determined by visual observation.

From Table II it will be noted that vinylidene chloride and chloroform used in Examples 8 and 10, respectively, had very little effect on the solvent or the aluminum coupons. In example 12 a pronounced effect on both the color of the solvent and on the aluminum coupons indicated the methylene chloride was degraded by the trans-dichloroethylene and the carbon tetrachloride. The stabilizing effect of tetrahydrofuran will be noted in Example 13. Whereas in Example 12 the solvent became discolored and there was corrosion loss in the aluminum coupons the tetrahydrofuran in Example 13 kept the solvent stabilized against degradation as evidenced by the solvent remaining clear and colorless and no loss in the weight of the aluminum coupons.

In Example 14 deterioration of the solvent system occurred due to the reaction of aluminum with the contained 1,1,1-trichloroethane. In Examples l5, l6 and 17 the addition of tetrahydrofuran and the combination of tetrahydrofuran and propylene oxide to this solvent system prevented such deterioration even after about 0.04 grams anhydrous aluminum chloride was added and the system refluxed an additional two days. In Example 18 even with the further addition of about 0.04 grams anhydrous ferric chloride and an additional five days of refluxing no corrosion of aluminum coupons in the flask or the condenser was observed.

tetrahydrofuran and propylene oxide were admixed with the methylene chloride containing the stabilized 1,1,1-trichloroethane was degradation of the methylene chloride prevented.

In Examples 19 to 26 of Table III, below, the aluminum reflux stability tests consisted of placing 190 ml of technical grade methylene chloride in a 300 ml flask, adding about 0.5 grams of 20 mesh aluminum and suspending a bright aluminum coupon about 2 X 7 cm. in a condenser fitted to the flask. Methylene chloride and the solvent containing durene, mesitylene and combinations of mesitylene with tetrahydrofuran and propylene oxide and with only tetrahydrofuran were refluxed for varying time periods. In all the tests the pH and acid content, as HCl were determined and visual observation of the aluminum condenser coupon were made at the completion of the test. The results of these tests are set forth in Table III below.

compound, durene (tetramethyl benzene) when refluxed with aluminum.

TABLE III EFFECT OF AROMATIC COMPOUNDS ON ALUMINUM- REFLUX STABILITY TESTS WITH METHYLENE CHLORIDE Condenser Example Volume Days Acid as Color Coupon N0. Solvent System Additive Test pH ppm HCI Solvent Corrosion l9 Methylene Chloride O 3 7.0 None Clear & Blisters Colorless 2O Methylene Chloride 5. Mesitylene 5 3 Fuming Orange- General (Trimethyl HCI Black severe Benzene) 21 Methylene Chloride 5, Mesitylene l4 7.l None Clear & None 0.25 wt. of Tetracolorless hydrofuran 22 Same as Example 21 5. Mesitylene 17 4.8 3,000 Brown, General with addition of about 0.04 grams AICI and three additional days of reflux. 23 Methylene Chloride 5 Mesitylene l4 7.1 None Clear. None 0.25 wt. Tetrahydro gray furan 0.25 wt. Propylene Oxide 24 Example 23 after 5, Mesitylene 17 6.5 3 Clear, None addition of about gray 0.04 grams of anhydrous AlCl and three additional days of reflux. 25 Methylene Chloride 5, Durene 5 Pink Purple (Tetramethyl Blisters Benzene) 26 Example 25 after 5, Durene 6 5.4 I08 Yellow. General one additional day turbid severe of reflux.

The tests in both Tables II and III were conducted by Although the present invention has been described venting the condenser to room air and without the adwith detailed reference to specific embodiments theredition of water. Also in Tables II and Ill the pH deterof, it is not intended to be so limited since modificaminations were made with a portion of the water layer tions and alterations may be made therein which are obtained by extraction of the solvent with water equal within the complete intended scope of this invention as to the volume of the solvent system. defined by the appended claims.

What is claimed is:

Table In lnustfates the Prevemlon of dfigradatlon of l. A stabilized methylene chloride composition conmethylene Chlorlde y 'tetrahydl'ofuran the Presence sisting essentially of methylene chloride and stabilizing of aluminum and aluminum chloride and the aromatic amounts f from about ()5 to about 31 percent by Compound mesitylene In Examples 2] and 22, and y weight of the methylene chloride of each oltetrahydrothe combination of tetrahydrofuran and propylene furan d propylene Oxidc oxide in the presence of mesitylene (trimethyl ben- 2. The composition of claim 1 wherein from about zene) aluminum and aluminum chloride in Examples 0.10 to about 1.0 percent by weight of each ol'tetrahy- 23 and 24. Examples 25 and 26 show degradation of drofuran and propylene oxide is present. methylene chloride in the presence of another aromatic 

2. The composition of claim 1 wherein from about 0.10 to about 1.0 percent by weight of each of tetrahydrofuran and propylene oxide is present. 